A/c Question

We own a 93 Lumina 3.1. It has an R12 A/C unit on it. I wanted to know how to jump the low pressure switch to see if the compressor works? Most compressors have two posts that you can jump across to bypass the switch. The Lumina is a single post. If it works then I want to charge it. I have R12 & an EPA Type I & II certification. I use to work commerical refrigeration.
Any help would be appreciated.

I don't have my texts with me but a quick search on Google should turn something up. I'll look it up in detail tomorrow at the shop. But I believe with single post switches it's just a short to ground.

I don't have my texts with me but a quick search on Google should turn something up. I'll look it up in detail tomorrow at the shop. But I believe with single post switches it's just a short to ground.

So if I grounded the switch it would be like jumping was before. I noticed the other day that there is a 3 post switch by the filter/dryer, but I believe it has to do with idle with A/C on because I was fooling with it on day & blew an ignition fuse, causing the idle to stay at about 2000 RPMs, When I replaced the fuse I discovered the A/C relay was missing. I replaced that also with a new one. I'll fool with it some more and keep you posted. Any further info would be greatly appreciated
Thanks

So if I grounded the switch it would be like jumping was before. I noticed the other day that there is a 3 post switch by the filter/dryer, but I believe it has to do with idle with A/C on because I was fooling with it on day & blew an ignition fuse, causing the idle to stay at about 2000 RPMs, When I replaced the fuse I discovered the A/C relay was missing. I replaced that also with a new one. I'll fool with it some more and keep you posted. Any further info would be greatly appreciated
Thanks
i went thru what your trying to do.. you cant jump the switch.. just keep the car runing and put the r12 in it , the compresser will kick on ..

We own a 93 Lumina 3.1. It has an R12 A/C unit on it. I wanted to know how to jump the low pressure switch to see if the compressor works? Most compressors have two posts that you can jump across to bypass the switch. The Lumina is a single post. If it works then I want to charge it. I have R12 & an EPA Type I & II certification. I use to work commerical refrigeration.
Any help would be appreciated.

you should first pressure test the system with nitrogen for leaks.....if there are leaks and this system has been unused for a period of time the oil must be replaced as it will be contaminated.... then with all this done pump down the system for 8hrs.....shut down pump and see if it holds vacuum then with r12 hooked up to gauges allow liquid refrigerent to enter the high side put in one pound... then start engine and slowly fill on low side gas until pressures/capacity reached....compressor will start as there will be pressure unless compressor saftey is blown.....but you should already now this anyway!!!!

Those three wire switches you are wanting to jump are pressure transducers- they mesure pressure- if you try to jump one you will fry something-- just remember- you don't jumper three wire "switches"

Thanks for the input. I'm well versed on charging A/C systems. I just wasn't sure how to check the compressor for operation. But it sounds like it will automatically start when pressures are correct. The old units in some cases had to be jumped to charge if empty, or low enough to open the low pressure switch until presures came up to allow the low pressure switch to close. When you pulled a vacuum you could sometimes get enough freon in to do that but not always. Thanks for the info I will keep you posted on what I find. I'm not going to get to it for awhile I have a busy few weeks.